Linux see 20GB ram instead of 24 GB

Question

I used to have two RAM sticks, of 8GB each. I switched one of them for a 16G stick, and expected I would now have a total of 24GB but I have 20GB instead. The result of free -h:

              total        used        free      shared  buff/cache   available
Mem:           19Gi       2.8Gi        12Gi       105Mi       3.9Gi        16Gi
Swap:         2.0Gi          0B       2.0Gi

cat /proc/meminfo

MemTotal:       20292048 kB
MemFree:        13254056 kB
MemAvailable:   16923208 kB
Buffers:          269448 kB
Cached:          3706108 kB
SwapCached:            0 kB
Active:          1319968 kB
Inactive:        4874796 kB
Active(anon):      14752 kB
Inactive(anon):  2312796 kB
Active(file):    1305216 kB
Inactive(file):  2562000 kB
Unevictable:         132 kB
Mlocked:             132 kB
SwapTotal:       2097148 kB
SwapFree:        2097148 kB
Dirty:               524 kB
Writeback:             0 kB
AnonPages:       2219512 kB
Mapped:          1341800 kB
Shmem:            108248 kB
KReclaimable:     159592 kB
Slab:             372516 kB
SReclaimable:     159592 kB
SUnreclaim:       212924 kB
KernelStack:       23104 kB
PageTables:        56624 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    12243172 kB
Committed_AS:   13539940 kB
VmallocTotal:   34359738367 kB
VmallocUsed:       67940 kB
VmallocChunk:          0 kB
Percpu:            25088 kB
HardwareCorrupted:     0 kB
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
FileHugePages:         0 kB
FilePmdMapped:         0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
Hugetlb:               0 kB
DirectMap4k:      635844 kB
DirectMap2M:    10717184 kB

sudo dmidecode -t memory

    Getting SMBIOS data from sysfs.
SMBIOS 3.3.0 present.
# SMBIOS implementations newer than version 3.2.0 are not
# fully supported by this version of dmidecode.
Handle 0x0022, DMI type 16, 23 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: None
    Maximum Capacity: 64 GB
    Error Information Handle: 0x0025
    Number Of Devices: 2
Handle 0x0023, DMI type 17, 92 bytes
Memory Device
    Array Handle: 0x0022
    Error Information Handle: 0x0026
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 16384 MB
    Form Factor: SODIMM
    Set: None
    Locator: DIMM 0
    Bank Locator: P0 CHANNEL A
    Type: DDR4
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 3200 MT/s
    Manufacturer: Unknown
    Serial Number: E81F0ECB
    Asset Tag: Not Specified
    Part Number: CT16G4SFRA32A.M16FR
    Rank: 2
    Configured Memory Speed: 3200 MT/s
    Minimum Voltage: 1.2 V
    Maximum Voltage: 1.2 V
    Configured Voltage: 1.2 V
    Memory Technology: DRAM
    Memory Operating Mode Capability: Volatile memory
    Firmware Version: Unknown
    Module Manufacturer ID: Bank 6, Hex 0x9B
    Module Product ID: Unknown
    Memory Subsystem Controller Manufacturer ID: Unknown
    Memory Subsystem Controller Product ID: Unknown
    Non-Volatile Size: None
    Volatile Size: 16 GB
    Cache Size: None
    Logical Size: None
Handle 0x0024, DMI type 17, 92 bytes
Memory Device
    Array Handle: 0x0022
    Error Information Handle: 0x0027
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 8192 MB
    Form Factor: SODIMM
    Set: None
    Locator: DIMM 0
    Bank Locator: P0 CHANNEL B
    Type: DDR4
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 3200 MT/s
    Manufacturer: Samsung
    Serial Number: 00000000
    Asset Tag: Not Specified
    Part Number: M471A1G44AB0-CWE

    Rank: 1
    Configured Memory Speed: 3200 MT/s
    Minimum Voltage: 1.2 V
    Maximum Voltage: 1.2 V
    Configured Voltage: 1.2 V
    Memory Technology: DRAM
    Memory Operating Mode Capability: Volatile memory
    Firmware Version: Unknown
    Module Manufacturer ID: Bank 1, Hex 0xCE
    Module Product ID: Unknown
    Memory Subsystem Controller Manufacturer ID: Unknown
    Memory Subsystem Controller Product ID: Unknown
    Non-Volatile Size: None
    Volatile Size: 8 GB
    Cache Size: None
    Logical Size: None

Linux: Ubuntu 20.04.6 LTS

Is there something I can do to see all of my RAM or is this a hardware issue?

UPD journalctl -b0 -k logs:

    BIOS-provided physical RAM map:
BIOS-e820: [mem 0x0000000000000000-0x000000000009efff] usable
BIOS-e820: [mem 0x000000000009f000-0x00000000000bffff] reserved
BIOS-e820: [mem 0x0000000000100000-0x0000000009efffff] usable
BIOS-e820: [mem 0x0000000009f00000-0x0000000009f0efff] ACPI NVS
BIOS-e820: [mem 0x0000000009f0f000-0x00000000b89e8fff] usable
BIOS-e820: [mem 0x00000000b89e9000-0x00000000babe8fff] reserved
BIOS-e820: [mem 0x00000000babe9000-0x00000000c8dfefff] usable
BIOS-e820: [mem 0x00000000c8dff000-0x00000000cbdfefff] reserved
BIOS-e820: [mem 0x00000000cbdff000-0x00000000cdf7efff] ACPI NVS
BIOS-e820: [mem 0x00000000cdf7f000-0x00000000cdffefff] ACPI data
BIOS-e820: [mem 0x00000000cdfff000-0x00000000cdffffff] usable
BIOS-e820: [mem 0x00000000ce000000-0x00000000cfffffff] reserved
BIOS-e820: [mem 0x00000000f8000000-0x00000000fbffffff] reserved
BIOS-e820: [mem 0x00000000fdc00000-0x00000000fdcfffff] reserved
BIOS-e820: [mem 0x00000000fe000000-0x00000000fe0fffff] reserved
BIOS-e820: [mem 0x00000000fec00000-0x00000000fec01fff] reserved
BIOS-e820: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
BIOS-e820: [mem 0x00000000fec20000-0x00000000fec20fff] reserved
BIOS-e820: [mem 0x00000000fed80000-0x00000000fed81fff] reserved
BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
BIOS-e820: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
BIOS-e820: [mem 0x0000000100000000-0x000000052e2fffff] usable
BIOS-e820: [mem 0x000000052e300000-0x000000062fffffff] reserved
extended physical RAM map:
reserve setup_data: [mem 0x0000000000000000-0x000000000009efff] usable
reserve setup_data: [mem 0x000000000009f000-0x00000000000bffff] reserved
reserve setup_data: [mem 0x0000000000100000-0x0000000009efffff] usable
reserve setup_data: [mem 0x0000000009f00000-0x0000000009f0efff] ACPI NVS
reserve setup_data: [mem 0x0000000009f0f000-0x00000000adb86017] usable
reserve setup_data: [mem 0x00000000adb86018-0x00000000adb93857] usable
reserve setup_data: [mem 0x00000000adb93858-0x00000000b2f69017] usable
reserve setup_data: [mem 0x00000000b2f69018-0x00000000b2f77057] usable
reserve setup_data: [mem 0x00000000b2f77058-0x00000000b89e8fff] usable
reserve setup_data: [mem 0x00000000b89e9000-0x00000000babe8fff] reserved
reserve setup_data: [mem 0x00000000babe9000-0x00000000c8dfefff] usable
reserve setup_data: [mem 0x00000000c8dff000-0x00000000cbdfefff] reserved
reserve setup_data: [mem 0x00000000cbdff000-0x00000000cdf7efff] ACPI NVS
reserve setup_data: [mem 0x00000000cdf7f000-0x00000000cdffefff] ACPI data
reserve setup_data: [mem 0x00000000cdfff000-0x00000000cdffffff] usable
reserve setup_data: [mem 0x00000000ce000000-0x00000000cfffffff] reserved
reserve setup_data: [mem 0x00000000f8000000-0x00000000fbffffff] reserved
reserve setup_data: [mem 0x00000000fdc00000-0x00000000fdcfffff] reserved
reserve setup_data: [mem 0x00000000fe000000-0x00000000fe0fffff] reserved
reserve setup_data: [mem 0x00000000fec00000-0x00000000fec01fff] reserved
reserve setup_data: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
reserve setup_data: [mem 0x00000000fec20000-0x00000000fec20fff] reserved
reserve setup_data: [mem 0x00000000fed80000-0x00000000fed81fff] reserved
reserve setup_data: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
reserve setup_data: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
reserve setup_data: [mem 0x0000000100000000-0x000000052e2fffff] usable
reserve setup_data: [mem 0x000000052e300000-0x000000062fffffff] reserved
e820: reserve RAM buffer [mem 0x0009f000-0x0009ffff]
e820: reserve RAM buffer [mem 0x09f00000-0x0bffffff]
e820: reserve RAM buffer [mem 0xadb86018-0xafffffff]
e820: reserve RAM buffer [mem 0xb2f69018-0xb3ffffff]
e820: reserve RAM buffer [mem 0xb321f000-0xb3ffffff]
e820: reserve RAM buffer [mem 0xb3351000-0xb3ffffff]
e820: reserve RAM buffer [mem 0xb89e9000-0xbbffffff]
e820: reserve RAM buffer [mem 0xc8dff000-0xcbffffff]
e820: reserve RAM buffer [mem 0xce000000-0xcfffffff]
e820: reserve RAM buffer [mem 0x52e300000-0x52fffffff]
[drm] vm size is 262144 GB, 4 levels, block size is 9-bit, fragment size is 9-bit
amdgpu 0000:05:00.0: amdgpu: VRAM: 4096M 0x000000F400000000 - 0x000000F4FFFFFFFF (4096M used)
amdgpu 0000:05:00.0: amdgpu: GART: 1024M 0x0000000000000000 - 0x000000003FFFFFFF
amdgpu 0000:05:00.0: amdgpu: AGP: 267419648M 0x000000F800000000 - 0x0000FFFFFFFFFFFF
[drm] Detected VRAM RAM=4096M, BAR=4096M
[drm] RAM width 128bits DDR4
[drm] amdgpu: 4096M of VRAM memory ready
[drm] amdgpu: 4096M of GTT memory ready.
[drm] GART: num cpu pages 262144, num gpu pages 262144
[drm] PCIE GART of 1024M enabled.
[drm] PTB located at 0x000000F400900000

when you had the two x 8GB - what did free -h output? Also, what CPU do you have? — Jaromanda X, Oct 19 '23 at 22:57
AMD Ryzen 7 5700U with Radeon Graphics, do not remember well, but it seems free -h showed something like 12-13 GB — vdkt, Oct 20 '23 at 05:48
As Jaromanda X points out, is it reasonable to expect that your system reserves 4 GB (for something) now, just like it did when you had 2*8 GB? — Kusalananda, Oct 20 '23 at 07:35
How I can check the system reserved RAM? I think it shouldn't reserve while I do nothing — vdkt, Oct 20 '23 at 09:08
@vdkt Check the boot logs, the kernel tells you what memory it sees and what part of it is usable: journalctl -b0 -k. If you see anything interesting regarding your question, please add the log lines to your question. — xhienne, Oct 20 '23 at 10:38
How much memory is assigned to the built-in graphics card? You should be able to check this in BIOS. — Gerald Schneider, Oct 20 '23 at 11:41
I've executed journalctl -b0 -k and attached the logs I think related to the questions. But my knowledge does not allow me make a decision is it expected. — vdkt, Oct 20 '23 at 13:00
I am no specialist, but from https://askubuntu.com/questions/1330514/how-to-check-ram-channel I would say that your memory in configured in dual channel, so maybe your hardware does not support dual channel with heterogeneous sticks. — Vincent Nivoliers, Oct 20 '23 at 13:12
@VincentNivoliers, thank you, I've check this topic and ran command sudo dmidecode -t memory. This is the output: Bank Locator: P0 CHANNEL A Bank Locator: P0 CHANNEL B — vdkt, Oct 20 '23 at 13:23
One more thing about this I would say that your memory in configured in dual channel, so maybe your hardware does not support dual channel with heterogeneous sticks There is only one RAM slot and it contains 16GB stick. The other RAM memory is inbuilt. Maybe it can help — vdkt, Oct 20 '23 at 13:27

score 3 · Accepted Answer · answered Oct 20 '23 at 18:22

According to your posted logs and described behavior, I believe your AMD Ryzen 7 5700U is also an integrated graphics card which does not have its own RAM.

There may be an option in your BIOS to adjust the integrated graphics VRAM which will take RAM away from your installed system RAM.

Your logs currently show that 4096M is allocated to your integrated graphics VRAM, so you could expect that amount of RAM to not be available to your system.

Linux see 20GB ram instead of 24 GB

1 Answers1